docs: def add_user(self, username, password, group, sharable=True,
                   reserved=False, memo=None):
          """
          Params:
              username - username for user
              password - password for user
              group - string the range is "admin" and "user". In different group,
                      the user has different authorities.
  
              sharable - bool, true means allow multi-point login
  
              reserved - bool, true means this user can't be deleted
  
              memo - memo to user
          """
  
          cmd = "userManager.cgi?action=addUser&user.Name={0}" \
                "&user.Password={1}&user.Group={2}&user.Sharable={3}" \
                "&user.Reserved={4}".format(
                    username, password, group.lower(), sharable.lower(),
                    reserved.lower())
  
          if memo:
              cmd += "&user.Memo=%s" % memo
  
          ret = self.command(cmd)
          return ret.content.decode('utf-8')